The response of mitochondria to hypoxia/ischemia in cellular systems will be compared to that of mitochondria in the soleus muscle cells of live rats to test an apparent discrepancy between the two model systems of the deleterious effects of ischemia reperfusion. Measurements in cellular systems will be carried out in Lubliana, Slovenia, spin trapping will be accomplished during a 3 month visit to the division of Transplant Surgery at the University of Innsbruck and EPR oximetry will be accomplished in vivo during a 9 month visit to Dartmouth.